1. Field of the Invention
This invention relates to a thin film magnetic head, a magnetic head device and a magnetic recording/reproducing device.
2. Related Art Statement
A composite type magnetic head comprised of a writing element and a reading element with a giant magnetoresistive effective film (hereinafter, called as a “GMR film”) is employed as a thin film magnetic head to be utilized in a magnetic disk drive device of a computer memory unit.
As the writing element is employed an inductive type electromagnetic conversion element, which is formed on the reading element. The inductive type electromagnetic conversion element is comprised of a bottom magnetic film, a top magnetic film, a coil film supported by a gap film, an insulating film and the like.
The forefronts of the bottom magnetic film and the top magnetic film are composed of a bottom pole piece and a top pole piece, respectively, which are opposed to each other via the gap film with a minute thickness and whereby writing process is carried out. The bottom magnetic film and the top magnetic film have their respective yoke portions which are magnetically connected at a back gap portion which is located at the rear side from the top pole piece and the bottom pole piece so that the magnetic films complete a magnetic circuit. The coil film is so formed as to wind the back gap portion.
As the GMR film constituting the reading element are typically exemplified a spin valve film (hereinafter, called as a “SV film”) and a ferromagnetic tunnel junction film (hereinafter, called as a “TMR film”). The reading element made of the GMR film can realize reading performance of high resolution not depending on the relative velocity for a magnetic disk.
In order to realize high recording performance using such a thin film magnetic head as mentioned above, it is required that the amount of data to be stored in the magnetic disk per unit area (the surface recording density of the magnetic disk) is developed. The high surface recording density can be realized by enhancing the performance of the writing element, the performance of the magnetic recording medium such as the magnetic disk, and the high frequency performance of the writing circuit.
With the writing element, if the gap length between the pole pieces is decreased, the surface recording density can be developed. The decrease of the gap length is restricted on the decrease in magnetic recording intensity between the pole pieces.
With the magnetic disk, if the data track number is increased, the surface recording density can be developed. The track number of the magnetic disk is represented by “TPI” (Track Per Inch). The TPI performance of the writing element can be developed by downsizing the dimension of the writing head to define the data track width. The dimension of the writing head is usually called as a “head track width”.
In order to realize high recording density in HDDs to be employed in computers, the track width is narrowed, e.g., to 0.4 μm and 0.3 μm, particularly 0.2 μm at present. With the narrowed track width, it becomes important how to reduce the influence of the magnetic field leaked from the both edges of the pole pieces in the track width direction for the magnetic disk, which is called as “side fringe”, in addition to the overwrite performance.
In order to realize the overwrite performance, the pole pieces are made of a high saturated magnetic flux density material and the configurations of the pole pieces are optimized. In order to reduce the side infringe in the track width direction, such a technique is proposed as to match the width of the bottom pole piece to the width of the top pole piece by means of ion beam milling to form the same track width from the bottom pole piece and the top pole piece (cf., Patent Publications No. 1 and No. 2).
For the same sake, such a technique is proposed as to form tapered portions between the zero throat points and the enlarged portions of the bottom magnetic film and the top magnetic film (cf., Patent Publication No. 3).
For the same sake, such a technique is proposed as to set the width of the top yoke portion larger than the width of the top pole piece to project both edges of the top yoke portion from both edges of the top pole piece in the width direction (cf., Patent Publication No. 4)
With the above-mentioned conventional technique, however, if the track width is narrowed to 0.3 μm or below, the adjacent tracks may be erased, so that the side fringe can not be eliminated sufficiently.
Patent Publication No. 1: Japanese Patent Application Laid-open No. 7-262519
Patent Publication No. 2: Japanese Patent Application Laid-open No. 7-225917
Patent Publication No. 3: U.S. Pat. No. 5,600,519
Patent Publication No. 4: U.S. Pat. No. 5,452,164